INSPIRE Scholarship – Chemistry
S‑Block & P‑Block Elements
1️⃣ Simple Explanation
| Block | Placement in the Periodic Table | Main Features | Typical Oxidation States | Representative Elements |
|---|---|---|---|---|
| S‑Block | Groups 1–2 (alkali & alkaline‑earth metals) | One or two valence electrons, highly reactive, low ionisation energies | +1 (Group 1), +2 (Group 2) | Li, Na, K, Ca, Sr, Ba |
| P‑Block | Groups 13–18 (including halogens, noble gases) | Valence electrons in s and p orbitals, varied chemistry, includes metals, non‑metals, and metalloids | +3, +2, +1, 0, –1, –2, –3 (depends on element) | C, N, O, F, Cl, Si, P, S, Ar, etc. |
Key Idea
- S‑Block elements are metals that readily lose 1–2 electrons to form simple ionic salts.
- P‑Block elements are a diverse group: metals, non‑metals, and metalloids. Their chemistry is governed by the filling of both s and p orbitals, giving rise to a wide variety of oxidation states and bonding patterns.
2️⃣ S‑Block Elements
| Property | Details |
|---|---|
| Electron configuration | ns^1 (Group 1) or ns^2 (Group 2) |
| Physical | Soft, shiny, low melting/boiling points, highly ductile |
| Chemical | Extremely reactive; form +1 (alkali) or +2 (alkaline‑earth) cations; give bright flames (Na → yellow, K → lilac) |
| Common compounds | Alkali metal hydroxides (NaOH, KOH), oxides (Na₂O, CaO), halides (NaCl, CaCl₂) |
| Typical uses | Table salt (NaCl), fertilizers (CaCO₃), batteries (Li‑ion), soaps (Na₂SO₄, K₂CO₃) |
Trend: Ionisation energy ↓ down a group; metallic character ↑ down a group.
3️⃣ P‑Block Elements
| Property | Details |
|---|---|
| Electron configuration | ns^2 np^1‑6 (varies per group) |
| Physical | Metals (e.g., Al), non‑metals (e.g., S, N), metalloids (Si, Ge) |
| Chemical | Oxidation states vary from +3 to –3; form covalent/ionic bonds; halogens are highly electronegative |
| Common compounds | Halides (NaCl, KBr), oxides (SiO₂, Al₂O₃), sulfides (FeS), nitrides (TiN) |
| Typical uses | Electronics (Si wafers), glass (SiO₂), catalysts (Al₂O₃), pigments (CuSO₄), pharmaceuticals (C₆H₁₀O₅) |
Trend:
- Electronegativity ↑ left → right, ↓ period.
- Ionisation energy ↑ left → right, ↓ period.
- Enthalpy of formation varies with oxidation state.
4️⃣ Key Points (Quick Takeaway)
| # | S‑Block | P‑Block |
|---|---|---|
| 1 | One valence electron (Group 1) or two (Group 2) → easy loss → +1 or +2 ions | Valence electrons in s & p → wide range of oxidation states |
| 2 | Very low ionisation energies; form ionic salts | Oxidation states depend on electron configuration; halogens have +1, +3, +5, +7 |
| 3 | Metallic: high density, good conductors | Diverse: metals, non‑metals, metalloids |
| 4 | Good flame tests: Na → yellow, K → lilac, Ca → orange‑red | Halogens show distinct colours: F (yellow‑green), Cl (yellow), Br (red‑brown), I (violet) |
| 5 | Highly reactive with water → vigorous reactions | Halogens react with metals to form ionic halides (MCl) |
| 6 | Commonly used in batteries (Li, Na) and fertilizers (Ca) | Silicon for semiconductors; sulfur for vulcanisation; oxygen for combustion |
5️⃣ Worked Example
Predict the products and major oxidation states when Lithium reacts with water.
-
Identify the element & group
- Lithium (Li) – Group 1, S‑block → oxidation state +1.
-
Write the unbalanced equation
[ \text{Li} + \text{H}_2\text{O} \rightarrow ? ] -
Determine the reaction type
- Alkali metal + water → metal hydroxide + hydrogen gas.
-
Balance the equation
[ 2,\text{Li} + 2,\text{H}_2\text{O} \rightarrow 2,\text{LiOH} + \text{H}_2\uparrow ] -
Check oxidation states
- Li: +1 (in LiOH)
- H in water: +1 → in LiOH: +1 (no change)
- H₂ gas: 0 (reduced).
- O remains –2 throughout.
**Conclusion